A low-cost method of feeding PAC is to use a _____ where precise feed in ____

A low-cost method of feeding PAC is to use a _____ where precise feed in ____

• A. Helix-type feeder, primary
• B. Helix-type feeder, secondary
• C. Slurry feed system, primary
• D. Slurry feed system, secondary

Answer: (B)

The idea is to meter a solid coagulant like PAC with a simple, reliable device after the rapid-mix stage. A helix-type (screw) feeder is a straightforward, low-cost way to deliver a controlled amount of PAC powder or slurry into the water stream. Placing this dosing point in the secondary stage—after rapid mixing—takes advantage of calmer flow and better mixing conditions, allowing the chemical to distribute evenly and react effectively with the particles. In the primary stage, the high turbulence can make uniform dispersion of a dry PAC difficult and may require a more complex slurry prep and feed system, which adds cost. So, using a helix-type feeder in the secondary stage provides precise feed at lower cost while promoting proper coagulation.

The idea is to meter a solid coagulant like PAC with a simple, reliable device after the rapid-mix stage. A helix-type (screw) feeder is a straightforward, low-cost way to deliver a controlled amount of PAC powder or slurry into the water stream. Placing this dosing point in the secondary stage—after rapid mixing—takes advantage of calmer flow and better mixing conditions, allowing the chemical to distribute evenly and react effectively with the particles. In the primary stage, the high turbulence can make uniform dispersion of a dry PAC difficult and may require a more complex slurry prep and feed system, which adds cost. So, using a helix-type feeder in the secondary stage provides precise feed at lower cost while promoting proper coagulation.